The exemplary embodiment relates to printing systems. It finds particular application in connection with a viewing system which enables viewing of a print job in progress, and will be described with particular reference thereto.
Electronic printing systems typically employ an input terminal which receives images in digital form and conversion electronics for converting the image to image signals or pixels. The printing system may include a scanner for scanning image-bearing documents or be connected to a computer network which supplies the digital images. The signals are stored and are read out successively to a marking engine for formation of the images and transfer of the images to a print medium, such as sheets of paper. In a typical xerographic (electrostatographic) marking engine, a photoconductive insulating member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing material. Generally, the developing material comprises toner particles adhering triboelectrically to carrier granules. The developed image is subsequently transferred to the print medium. The fusing of the toner onto paper is generally accomplished by applying heat to the toner with a heated roller and application of pressure. In multi-color printing, successive latent images corresponding to different colors are recorded on the photoconductive surface and developed with toner of a complementary color. Each toner is associated with a separate developer station and applied to the photoreceptor in sequence. The single color toner images are successively transferred to the copy paper to create a multi-layered toner image on the paper. The multi-layered toner image is then permanently affixed to the copy paper in the fusing process.
For large scale printers, the sheets which constitute a print job may travel along a lengthy paper path, passing through one or more marking engines as well as other components, such as paper feeders, inverters, stackers, bookbinders, and the like, before being finally output. Many pages of the print job may thus be in progress in the printing system before the first pages of a job or assembled document copy are output. If there is an error in the print job, such as incorrect image content, incorrect sheet orientation, or even an incorrect document selected for the print job, the operator may not be aware of the error until the first few copies of the job are output.
The operator has no ready way of viewing a print job in progress to determine if such visible errors are occurring. The marking engine is enclosed within a housing cabinet which is designed to shield the photoreceptor from all light, other than the light used in exposure of the images. Typically the system is configured such that, if a door to the cabinet is opened, the current print job in progress is stopped. Since the opening of the door can allow light to enter and have a deleterious effect on the pages being printed, some or all of the pages may need to be reprinted once the door is closed and the system returned to an operational state. Thus, an operator avoids opening the door to view the job in progress.